The technology described herein relates to systems and methods for preparing epitaxially textured polycrystalline films.
In recent years, various laser crystallization techniques for crystallizing or improving the crystallinity of an amorphous or polycrystalline semiconductor film have been investigated. Laser crystallization has been used in the manufacture of a variety of devices, such as image sensors and displays, for example, active-matrix liquid-crystal display (AMLCD) devices. In the latter, a regular array of thin-film transistors (TFTs) are fabricated on an appropriate transparent substrate and each transistor serves as a pixel controller. Large grain polycrystalline thin-films also have been used as seed layers for polycrystalline thick-film solar cells.
Laser-induced crystalline growth in thin film semiconductors, while improving location and size of the crystalline structure, can nonetheless lead to a material with an intragrain defect density that is unacceptably high for certain microelectronics and solar cell applications. Depending on experimental conditions, including the growth velocity, film thickness and details of the irradiation, the defects can range anywhere from closely spaced stacking faults or twin boundaries, to widely spaced sub-boundaries, e.g., several μm apart
In addition, the crystal orientation of the seed can influence defect formation. For example, in pulsed-laser irradiation experiments, it is commonly found that {111} and in particular {100} surface orientations typically can lead to a minimally defective material, and other orientations, such as {110} or {112} can lead to defective growth in one or more lateral growth directions. Conventional methods of obtaining a surface-oriented film (also referred to as a textured film) are known, including zone melt recrystallization (ZMR), solid phase recrystallization, direct deposition techniques (including, chemical vapor deposition (CVD) sputtering, and evaporation), surface-energy-driven secondary grain growth (SEDSGG) and pulsed laser crystallization (SLS, multiple-pulse excimer laser annealing (ELA)) methods.